Multiple Sclerosis (MS) is a chronic neurological disease of the central nervous system characterized by multifocal inflammation, demyelination and axonal damage. The disease process shows inflammation resulting in multiple patches of demyelination in MRI analyses of CNS. MS shows a high-degree of individual variability in the severity and progress of the disease. The diagnosis of MS is still mainly based on the characteristic clinical symptoms. There are no specific laboratory tests for MS. However, changes in MRI and presence of oligoclonal IgG bands in the cerebrospinal fluid are used as supporting findings for the clinical diagnosis. In spite of extensive research, the basic molecular events in the initiation and progression of MS are still poorly understood. Most MS cases are sporadic, but family twin and adoption studies indicate a strong genetic component in the pathogenesis of the disease. As in most complex diseases, the genetic contribution, although important, is by no means the sole determinant, but environmental, so far unidentified, factors contribute to the pathogenesis. Due to the evident genetic contribution in MS, we hypothesize that distinct allelic variations predispose to MS. We further hypothesize that well-characterized, ethnically-homogenous populations provide advantages in identification of genetic variations predisposing to complex traits, such as MS. Thus, we aim to identify gene variants predisposing to MS. We will focus on genetic loci, which we have previously identified in a genome-wide scan and now restricted to a few megabases. Our strategy is to utilize the unique, ethnically homogenous population sample of Finnish MS families. More specifically, we aim to: 1) Restrict chromosomal loci linked to MS by monitoring for association and linkage disequilibrium, in MS alleles using multiple single nucleotide polymorphisms in the critical regions on chromosomes-5 and -17; 2) monitor differential expression of genes located on the critical region of Chr.-5 and -17 using expression microarrays; and 3) sequence candidate genes selected in Aims 1 and 2 to detect allelic variants contributing to MS, and test these allelic variants in a study sample from more heterogeneous populations.